In certain instances, an aircraft actuation system can include a translating nut mechanism; that is, a mechanical device containing an externally-threaded shaft (referred to herein as a “screw shaft”), which rotates to drive the linear movement of a translating nut along the screw shaft. As a specific example, aircraft engine are often equipped with Variable Bleed Valve (VBV) systems, which include a particular type of translating nut mechanism referred to as a “bidirectional stop mechanism.” Within a given VBV system, the bidirectional stop mechanism may be coupled between a drive motor (e.g., a fuel-powered motor) and a number of bleed valves, which are linked by one or more flexible rods or “flex shafts.” During operation of the VBV system, the drive motor rotates the flex shafts to move the bleed valves between a range of positions and thereby control the rate at which airflow is bled from the main gas path of the engine. The bidirectional stop mechanism limits the rotational range of the flex shafts to prevent the drive motor from attempting to rotate the bleed valves beyond their fully closed or fully opened positions. In so doing, the bidirectional stop mechanism reduces component wear and decreases the likelihood of damaging the flex shafts, the bleed valves, and the other components of the VBV system.
Adequate lubrication is typically important to ensure proper and prolonged operation of a translating nut mechanism. In many cases, adequate lubrication can be provided by packing the translating nut mechanism with grease during original manufacture such that relubrication is seldom, if ever, required. In other cases, however, a translating nut mechanism may require relubrication at relatively frequent intervals. The lubrication requirements of a translating nut mechanism are highly dependent upon the operational demands placed on the mechanism, as well as the severity of the environmental conditions to which the mechanism is exposed. Consider, for example, a bidirectional stop mechanism of the type described above. In applications wherein movement of the translating nut and screw shaft are relatively limited, as may be the case wherein the nut is moved between a number of preset positions in accordance with commands issued by an analog engine controller, the bidirectional stop mechanism may require little to no relubrication over its service life. Conversely, relatively frequent relubrication or regreasing of the bidirectional stop mechanism may be appropriate when greater demands are placed on the mechanism due to, for example, usage in conjunction with a digital engine controller, which commands frequent, incremental movements of the shaft and nut. Unfortunately, the location and structural surrounding of the bidirectional stop mechanism can render relubrication a cumbersome and time consuming process potentially requiring removal and disassembly of the stop mechanism.
There thus exists an ongoing need to provide embodiments a VBV system including a bidirectional stop mechanism having lubricant enhancing features, which can decrease the frequency at which relubrication is required and/or facilitate relubrication of the mechanism without removal and overhaul during engine maintenance. More generally, it is desirable to provide embodiments of a translating nut mechanism offering one or more of the above-noted benefits and regardless of whether the mechanism assumes the specific form a bidirectional stop mechanism. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.